Only release buffer when a cursor is not in use and still spooling results

Author: fulghum

server/handler.go

@@ -673,9 +673,14 @@ func (h *Handler) resultForDefaultIter(ctx *sql.Context, c *mysql.Conn, schema s
 	timer := time.NewTimer(waitTime)
 	defer timer.Stop()
 
-	// Wrap the callback to include a BytesBuffer.Reset() to clean out rows that have already been spooled
+	// Wrap the callback to include a BytesBuffer.Reset() for non-cursor requests, to
+	// clean out rows that have already been spooled.
 	resetCallback := func(r *sqltypes.Result, more bool) error {
-		defer buf.Reset()
+		// A server-side cursor allows the caller to fetch results cached on the server-side,
+		// so if a cursor exists, we can't release the buffer memory yet.
+		if c.StatusFlags&uint16(mysql.ServerCursorExists) != 0 {
+			defer buf.Reset()
+		}
 		return callback(r, more)
 	}